The preparation of thermoplastically processable polyurethanes by the reaction of hydroxyl terminated polymers, organic diisocyanates and low molecular weight chain extenders has been practiced for some time. Particularly, it is disclosed in U.S. Pat. No. 3,523,101 that hydroxyl terminated polycaprolactones can be used to produce thermoplastic polyurethanes which form articles having excellent mechanical properties. It is known in the prior art that a variety of organic diisocyanates can be employed, such as, for example, bis(4-isocyanatophenyl) methane diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, isophorone diisocyanate, naphthalene diisocyanate, xylylene diisocyanate and the like. When bis(4-isocyanatophenyl)methane diisocyanate or hexamethylene diisocyanate is employed, as disclosed in U.S. Pat. No. 3,523,101, polyurethanes are obtained which may be thermoplastically processed to produce articles having good hardness and tensile strength. By comparison, thermoplastic polyurethanes produced by the aforementioned method using tolylene diisocyanate have usually exhibited poor mechanical properties when processed by conventional methods such as injection and compression molding. Generally, articles molded from tolylene diisocyanate based polyurethanes have not achieved an acceptable balance of tensile strength, stiffness and hardness to be used in a broad range of applications.
Due to the ready availability and low cost of tolylene diisocyanate, many efforts have been made to produce commercially acceptable thermoplastically processable polyurethane compounds based on tolylene diisocyanate. Resins produced by reacting tolylene diisocyanate, hydroxyl terminated polymers and low molecular weight chain extenders have been filled with as much as 30% by weight of reinforcing fillers such as carbon black to improve mechanical properties. While the room temperature tensile strength of articles molded from these materials was appreciably greater than that of articles molded from unfilled tolylene diisocyanate based polyurethanes, low and high temperature impact strength and heat distortion were such that often the materials were unsuitable for use in conventional molded or extruded products. Other attempts to produce thermoplastically processable tolylene diisocyanate based polyurethanes which produce formed articles having a good balance of mechanical properties have not been fully successful.